8 



PHYLUM TUNIC ATA ( UROCHORD A) . 



is an enlarged portion of the peribranchial groove and is called 

 the epibranchial groove (Fig. 6, fr f ). There is a considerable 

 interval, covered by a flat epithelium only, between it and the 

 first languet of the dorsal lamina (Fig 6 A). In some forms the 

 deflected part of the posterior ridge is of considerable length 

 (Fig. 6 B), reaching to the anterior end of the dorsal lamina, on 

 to which it is continuous. In such cases the epibranchial groove 

 may be very deep. It is lined by a ciliated epithelium similar 

 to that of the peripharyngeal groove of which it is an extension. 



FIG. 7. Transverse section through the endostyle of Clavelina lepadiformis, semidiagram- 

 matic (after Seeliger). ds dorsal ; ms median and vs ventral glandular band ; dfl dorsal 

 (marginal) ; mfl median ; vfl ventral ciliated band; en endoderm of lateral wall of pharynx : 

 mds median strip of flagellated cells. 



In some forms the anterior as well as the posterior face of the peri 

 pharyngeal furrow is ciliated. In Appendicularia and some synascidians 

 (e.g. Botryllus) the peripharyngeal band consists of a single ciliated ridge 

 only. 



The endostyle is a groove lined partly by glandular and partly 

 by ciliated cells extending the whole length of the median 

 ventral wall of the pharynx (Fig. 3). It presents but little 

 variation of structure. Typically it consists on each side of 

 three bands of large glandular cells, and of three bands of smaller 

 ciliated cells (Fig. 7). In the ventral middle line there is a narrow 

 band of small cells carrying long flagella. Anteriorly and pos- 

 teriorly the endostyle, excluding the marginal ciliated bands, 

 is continued into small blind pockets of the pharynx (Fig. 3), of 



